The present invention relates generally to cutting units for dry shavers and more particularly to a dry shaver of the type wherein the cutting unit reciprocally located within a perforated foil of the shaver. More specifically, the invention relates to a method and apparatus for forming the cutter strip of the cutting unit into a helical configuration. The cutting strip is of the type which is formed with undulations extending along the lengths of the strip and after formation into its helical pattern the strip is mounted upon a central longitudinal support member.
In the type of dry shaver to which the present invention relates, the perforated foil of the shaver is placed in contact with the skin and hair protruding through the perforations of the foil is cut by a shearing action which occurs between the cutting edge of the reciprocating cutter unit and the edges of the perforations.
An important consideration in such shavers requires that the cutter unit be arranged to operate in an efficient manner. It has been found that a cutter unit formed from a plurality of parallel blades mounted in a rigid support will operate efficiently. However, although such a cutter unit exhibits adequate efficiency, it involves an arrangement which has been found difficult and costly to manufacture.
In one method of construction offering some manufacturing advantages, a wire is wound on a mandrel having a circular cross section with subsequent grinding operation being performed to provide a cutting edge for the cutter unit. Cutters made in accordance with this prior art method have not, however, been found satisfactory primarily due to the fact that it is difficult to grind or otherwise provide a cutting edge in the unit. Furthermore, it has been found that the blades themselves develop inherent weaknesses.
Accordingly, there has been proposed a cutter unit for a dry shaver which involves utilization of an elongated strip which is wound edgewise into a helical configuration. The strip has undulations extending along the length thereof and the helically wound strip is mounted or embedded in a central longitudinal support member in order to form the cutter unit for the shaver.
The present invention relates to an improved method and apparatus for forming the undulated cutter strip of such a unit into a helix. The invention is directed to the provision of a cutter unit of this type which will exhibit superior operating characterists but which will not create adverse manufacturing problems.